Securing the choice of the network visited during roaming

ABSTRACT

A method for connecting a terminal outside the range of its home network, to a network of a visited area covered by a plurality of networks. The method includes sending a request relating to the connection, including an identifier relating to the visited area, receiving a response message to the request, including a list of at least one network of the plurality of networks, to which the terminal should connect in priority, disconnecting the terminal and connecting the terminal to the priority network of the list. A processing method includes receiving the request including an identifier relating to the visited area, obtaining, on the basis of the identifier, the list of at least one network from the plurality of networks, to which the terminal should connect in priority, and sending a response message to the request, including the list.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is continuation of U.S. application Ser. No.16/609,114, filed Oct. 28, 2019, which is a Section 371 National StageApplication of International Application No. PCT/FR2018/050997, filedApr. 20, 2018, and published as WO 2018/197790 A1 on Nov. 1, 2018, notin English, the entire contents of which are incorporated by referencetheir entireties.

FIELD OF THE INVENTION

The application for an invention lies in the field of mobilecommunications, and more particularly in the field of the roaming of asubscriber when abroad.

PRIOR ART

Mobile operators possess licenses to offer their services ingeographical areas generally limited to the territory of a country, orto a part of a country. Certain operators of different areas maynonetheless have roaming agreements which mutually favor theirrespective subscribers.

In this context, when a subscriber of an operator A is roaming in anarea covered by an operator B and by an operator C, and there exists afirst roaming agreement between operators A and B, and a second roamingagreement between operators A and C, but operator A prefers the firstroaming agreement, the objective is to contrive matters so that thesubscriber connects to the visited network of operator B. To this end, aconfiguration file is pushed to the SIM card of the subscriber'sterminal. This file comprises the list of the preferred networks ofoperator A, including that of operator B. It is then on the initiativeof the terminal to choose the preferred network, that is to say thenetwork of operator B, and not that of operator C, when it is in thearea common to these two operators.

The scheme adopted for pushing the configuration file in question isbased on SMS messages. The terminal's SIM card is updated following thereceipt of an SMS message. In order to prevent an operator other thanoperator A from updating the SIM card, the SMS must comprise a securitykey specific to the SIM card. This SMS is sent by operator A only whensame detects that its subscriber is roaming. It cannot be sent inadvance once and for all, before its subscriber exits its area, sincethe agreements between operators are very frequently modified, as afunction of the volumes of traffic that they exchange.

However, some visited operators circumvent this mechanism by detectingand blocking the update SMS. The subscriber's terminal no longerreceives the list of preferred operator networks, and selects theattachment network on the basis of other criteria, such as the power ofthe signal of a relay antenna, and this may unduly favor a network notforming part of the list.

One of the aims of the invention is to remedy these drawbacks of theprior art.

DISCLOSURE OF THE INVENTION

The invention seeks to improve the situation with the aid of a method ofconnecting a terminal beyond the range of its home network, to a networkof a visited area covered by a plurality of networks, the methodcomprising:

-   the sending of a request relating to the connection, comprising an    identifier relating to the visited area,-   the receipt of a message of response to the request, comprising a    list of at least one network of the plurality, to which the terminal    must connect by priority,-   the disconnection of the terminal and its reconnection to the    priority network of the list.

In contradistinction to the earlier technique, the home network of theterminal does not depend on a specific signaling, such as an SMS whosedelivery is not guaranteed, in order to communicate a list of preferredvisited networks to the terminal. The list is inserted into arequest-response exchange relating to the connection of the terminal toa first visited network. The home network recognizes the area in whichthe terminal is situated by virtue of an identifier, for example thePLMN identifier of the first visited network to which the terminal asksto attach itself, or has just attached itself. On receipt of a messagecomprising the list, which comprises a second visited network, preferredto the first by the home network, the terminal can prioritize thissecond network for any new connection, as long as it is beyond the rangeof its home network, that is to say while roaming.

According to one aspect of the connection method, the request is arequest for attachment of the terminal to a base station of the networkof the visited area.

In this embodiment, it is a request for attachment to the visitednetwork which triggers the receipt of the response comprising the list.The entity for managing the mobility in the visited area sends forexample a request for updating the location of the terminal, to a serverof the home network, able to manage rights and permissions for theterminal. The response to this request comprises the list.

According to one aspect of the connection method, the request is arequest for tracking area updating of the terminal.

In this embodiment, it is a request for tracking area updating whichtriggers the receipt of the response comprising the list. The entity formanaging the mobility in the visited area sends for example a requestfor updating the location of the terminal to a server of the homenetwork, able to manage rights and permissions for the terminal. Theresponse to this request comprises the list.

According to one aspect of the connection method, the list is encryptedand decryptable with a key previously shared between the terminal andthe home network.

In order to guarantee the integrity of the list, and to prevent thevisited network from modifying the list to its benefit, or delete it,this list can be encrypted with the aid of a key previously sharedbetween the terminal and its home network, for example a key of type Ki.Thus, if the terminal does not succeed in decrypting the list, or if thelist is absent from the expected response message, it can disconnectfrom the visited network, and recommence the connection method with adifferent visited network.

The various aspects of the connection method which have just beendescribed can be implemented independently of one another or incombination with one another.

The invention also relates to a method of processing a request relatingto the connection of a terminal beyond the range of its home network, toa network of a visited area covered by a plurality of networks, themethod comprising:

-   the receipt of the request comprising an identifier relating to the    visited area,-   the obtaining, on the basis of the identifier, of a list of at least    one network of the plurality, to which the terminal must connect by    priority,-   the sending of a message of response to the request, comprising the    list.

When a terminal is roaming, for example internationally, that is to saybeyond the range of its home network, it sends requests to an entity ofthe visited network, so as on the one hand to attach itself thereto, andthen on the other hand to establish and optionally to modify a sessionbetween the terminal and a gateway to a remote entity providing anapplication.

In a first exemplary initial request, the terminal sends to a basestation of the visited area an attachment request, which is transmittedby the base station to an entity for managing the mobility in thevisited area.

In a second exemplary initial request, the terminal, already attached,sends to the base station of the visited area an area update TAU request(Tracking Area Update), which is transmitted by the base station to themobility management entity.

This mobility management entity is for example an MME (MobilityManagement Entity) if the networks in question are 4G, and in bothcases, the terminal's initial request triggers other requests relatingto the connection of the terminal to the visited network, which are sentby the MME of the visited network to the home network. Such a requestrelating to the connection of the terminal to the visited network is forexample a request for location updating ULR (Update Location Request),or a session creation request CSR (Create Session Request).

Advantageously, the home network responds to this request by includingin the response message a list of preferred networks, without usingsignaling dedicated to this list, which would risk being detected assuch by the visited network, as may be for example the SMS dedicatedaccording to the earlier technique.

The fact of including the list of preferred networks runs counter to theprejudices of the person skilled in the art, since this list is an itemof information that does not respond directly to the request, but whichserves to anticipate a future connection of the terminal in the visitedarea.

Indeed, on receipt of the list, the terminal may decide to interrupt thecurrent connection so as to connect to one of the networks of the list,or on the contrary decide to remain connected and to wait for anotherevent in order to connect to one of the networks of the list, such asfor example the end of a session carried by the current connection, or achange of cell inside the visited area.

Moreover, the fact of using existing request and response messagessimplifies the implementation of the method in existing equipment. Inthis instance, only the response message is slightly modified withrespect to the existing one, by the addition of the list.

According to one aspect of the processing method, the request is arequest for attachment of the terminal to a base station (eNB) of thenetwork (vN-B) of the visited area.

When the terminal's initial request is an attachment request, the entityfor managing the mobility in the visited area sends a request forupdating the location of the terminal to a server of the home network,able to manage rights and permissions for the terminal. The response tothis request comprises the list.

According to one aspect of the processing method, the request is arequest for tracking area updating of the terminal.

When the terminal's initial request is a tracking area update, theentity for managing the mobility in the visited area sends a request forupdating the location of the terminal to a server of the home network,able to manage rights and permissions for the terminal. The response tothis request comprises the list.

According to one aspect of the processing method, the obtaining step ispreceded by a step of sending a request for location updating of theterminal.

In this first embodiment, whether the terminal's initial request be anattachment request or a tracking area update, the entity for managingthe mobility in the visited area uses a request for location updating ofthe terminal to obtain the list.

The entity for managing the mobility of the visited network thereforesends a request for updating the location of the terminal to a server ofthe home network, able to manage rights and permissions for theterminal.

This request triggers the obtaining of the list by the server of thehome network, and its sending to the entity for managing the mobility ofthe visited network.

For example, in 4G, a management entity MME for managing the visitednetwork sends a message ULR to an HSS server of the home network. Thismessage ULR comprises a parameter making it possible to identify thevisited area, for example a parameter Visited-PLMN-Id having thestructure of a PLMN (Public Land Mobile Network) parameter.

The HSS server obtains a list of preferred networks of the visited areafrom a database of the home operator. These networks are for exampleidentified by their PLMN. The HSS server inserts the list into a messageULA sent in response to the message ULR.

In its turn, the management entity MME obtains the list by extracting itfrom the message ULA, and inserts it into a message destined for theterminal, in response to the terminal's initial request.

In 5G, this may be an AMF (Access and Mobility Management Function)entity of the visited network which sends a message of location updatingof the terminal to a UDM (Unified Data Management) server of the homenetwork.

According to one aspect of the processing method, the obtaining step ispreceded by a step of sending a request for session creation ormodification.

In this second embodiment, whether the terminal's initial request be anattachment request or an area update request, the entity for managingthe mobility in the visited area uses, to obtain the list, a request forsession creation or modification. Here this entails a session, termedIP-CAN in 4G, between the terminal and an Internet access gateway, whichallows for example the terminal to exchange data with an applicationserver over the Internet.

The entity for managing the mobility of the visited network thereforesends a request for session creation or modification to a gateway of thehome network.

This request triggers the obtaining of the list and its sending, by thegateway of the home network.

In its turn, the management entity MME obtains the list by extracting itfrom the message sent by the gateway, and inserts it into a messagedestined for the terminal, in response to the terminal's initialrequest.

For example, in 4G, a management entity MME for managing the visitednetwork sends a message CSR to a PGW gateway (through an SGW) of thehome network. This message CSR comprises a parameter making it possibleto identify the visited area, for example the “Serving Network”parameter.

The PGW gateway obtains a list of networks of the visited area from aPCRF entity of the home operator. These networks are for exampleidentified by their PLMN.

In 5G, this may be an AMF entity of the visited network which sends amessage to an SMF (Session ManagementFunction) gateway of the homenetwork (through an SMF gateway of its own visited network) in order tocreate or modify a session between the terminal and the SMF gateway ofthe home network so as to join an application server.

It is therefore understood that in order that the terminal receives thelist of the preferred visited networks, the processing method which hasjust been described is implemented:

-   either in the mobility management entity MME of the visited network    (first embodiment),-   or in the mobility management entity MME of the visited network and    in the PGW gateway of the home network (second embodiment).

The invention also relates to a device for connecting a terminal beyondthe range of its home network, to a network of a visited area covered bya plurality of networks, the method comprising:

-   a sender configured to send a request relating to the connection,    comprising an identifier relating to the visited area,-   a receiver configured to receive a message of response to the    request, comprising a list of at least one network of the plurality,    to which the terminal must connect by priority,-   a processor configured to disconnect the terminal and reconnect it    to the priority network of the list.

This device, which implements in all its embodiments the connectionmethod which has just been described, is included in a mobile terminal.

The invention also relates to a device for processing a request relatingto the connection of a terminal beyond the range of its home network, toa network of a visited area covered by a plurality of networks, thedevice comprising:

-   a receiver configured to receive the request comprising an    identifier relating to the visited area,-   a processor configured to obtain, on the basis of the identifier, a    list of at least one network of the plurality, to which the terminal    must connect by priority,-   a sender of a message of response to the request, comprising the    list.

This device, which implements in all its embodiments the processingmethod which has just been described, can be included in a managemententity MME or in a PGW gateway between terrestrial mobile network and apacket switching network PDN, such as the Internet.

If the terrestrial mobile network is 5G, the device can be included inan AMF entity, or in an SMF gateway.

The invention also relates to a system for processing a request relatingto the connection of a terminal beyond the range of its home network, toa network of a visited area covered by a plurality of networks, thesystem comprising:

-   the plurality of networks of the visited area,-   the home network,-   at least one mobile terminal comprising a connection device such as    that which has just been described,-   at least one mobility management entity of the visited network,    comprising a processing device such as that which has just been    described.

According to one aspect of the processing system, it can also compriseat least one gateway of the home network comprising a processing devicesuch as that which has just been described.

The invention also relates to a computer program comprising instructionsfor the implementation of the steps of the connection method which hasjust been described, when this program is executed by a processor.

This program can use any programming language, and be in the form ofsource code, object code, or of code intermediate between source codeand object code, such as in a partially compiled form, or in any otherdesirable form.

The invention is also aimed at an information medium readable by amobile terminal, and comprising instructions of a computer program suchas is mentioned hereinabove.

The invention also relates to a computer program comprising instructionsfor the implementation of the steps of the processing method which hasjust been described, when this program is executed by a processor.

This program can use any programming language, and be in the form ofsource code, object code, or of code intermediate between source codeand object code, such as in a partially compiled form, or in any otherdesirable form.

The invention is also aimed at an information medium readable by amobility management entity or by a gateway between terrestrial mobilenetwork and the Internet, and comprising instructions of a computerprogram such as is mentioned hereinabove.

The information mediums mentioned hereinabove can be any entity ordevice capable of storing the program. For example, such a medium cancomprise a storage means, such as a ROM, for example a CD ROM or amicroelectronic circuit ROM, or else a magnetic recording means, forexample a floppy disk or a hard disk.

Moreover, the information mediums can be a transmissible medium such asan electrical or optical signal, which can be conveyed via an electricalor optical cable, by radio or by other means. One of the programsaccording to the invention can be in particular downloaded over anetwork of Internet type.

Alternatively, the information mediums can be an integrated circuit inwhich the program is incorporated, the circuit being adapted to executeor to be used in the execution of the methods in question.

PRESENTATION OF THE FIGURES

Other advantages and characteristics of the invention will become moreclearly apparent on reading the following description of a particularembodiment of the invention, given by way of simple illustrative andnonlimiting example, and of the appended drawings, among which:

FIG. 1 presents an overall view of the architecture elements allowingthe implementation of the proposed processing method,

FIG. 2 presents an exemplary implementation of the connection method andof the method of processing a request relating to the connection of aterminal while roaming, according to a first embodiment,

FIG. 3 presents an exemplary implementation of the connection method andof the method of processing a request relating to the connection of aterminal while roaming, according to a second embodiment,

FIG. 4 presents an exemplary structure of a device for connecting aterminal while roaming, according to one aspect of the invention,

FIG. 5 presents an exemplary structure of a device for processing arequest relating to the connection of a terminal while roaming,according to one aspect of the invention.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

In the subsequent description, examples are presented of severalembodiments based on a 4G mobile network architecture, but the inventionalso applies to other, earlier or forthcoming, architectures, such asfor example a 5G architecture.

FIG. 1 presents an overall view of the architecture elements allowingthe implementation of the proposed processing method.

Roaming agreements between operators allow a terminal beyond the rangeof its home network to connect, when it is within range of at least onevisited network.

More precisely, when the terminal UE, whose home network is the networkhN-A, is roaming in a visited area at least partially covered by avisited network vN-B, and it attaches itself to a base station eNB ofthe visited network vN-B, the mobility management entity vMME of thevisited network vN-B authenticates the terminal UE by interrogating thedatabase hHSS of the home network hN-A. The new location of the terminalUE is also communicated to a server of registers hHSS of the homenetwork hN-A, so that the terminal UE can be located by its homenetwork, for example for incoming calls.

Thereafter, a session, termed IP-CAN, is established for the terminal UEby the gateway hPGW of the home network hN-A, through at least onegateway vSWG of the visited network vN-B. The characteristics of thissession are determined by the function hPCRF of the home network hN-A,and are communicated to the terminal UE. For simplicity, a singlegateway is illustrated between the terminal UE roaming in the visitednetwork vN-B and the gateway hPGW of the home network hN-A, but severalmay be necessary.

The IP-CAN session thus established allows the terminal UE to exchangedata with any entity in a packet switching network PDN, such as forexample the Internet network, to which the gateway hPGW of the homenetwork hN-A is connected.

The visited area can also be at least partially covered by at least oneother terrestrial mobile network vN-C, not illustrated. The home networkhN-A may seek to balance, in terms of volume or in terms of cost, theoverall traffic with the networks of the visited area. Accordingly, itmust be able to inform the terminal about which visited network ispreferable.

FIG. 2 presents an exemplary implementation of the connection method andof the method of processing a request relating to the connection of aterminal while roaming, according to a first embodiment.

In this first embodiment, a list of preferred visited networks isprovided to the terminal by the home network during the phase ofupdating the location of the terminal.

In a known manner, during a step E10, the terminal UE sends the basestation eNB an attachment request AR. The base station eNB receives itduring a step E20 and sends during a step E21 a similar request to themobility management entity vMME, which receives it during a step E30.Other exchanges, not illustrated, take place thereafter, also in a knownmanner, where the visited network verifies and authenticates with thehome network the identity of the terminal UE.

During a step E31, once the terminal UE has been authenticated, themobility management entity vMME sends the server hHSS of the homenetwork hN-A a request ULR (Update Location Request) for locationupdating, in a known manner, for example by using the Diameter protocol.

During a step E40, the server hHSS receives the request ULR and performscustomary updating operations, for example with a mobility managemententity, not illustrated, of the home network hN-A.

In a novel manner, during a step E41, the server hHSS adds to themessage ULA (Update Location Acknowledgement) of acknowledgment of therequest ULR a list L of the networks that are preferred, at the time ofstep E41, by the network hN-A, and sends the acknowledgment message ULAto the mobility management entity vMME, for example by using theDiameter protocol. If it is not the server hHSS that holds the correctlist L, it obtains it for example on request from a so-called “roamingsteering” entity of the network hN-A.

This list L is preferably limited to the networks which cover the areaindicated in the request ULR, in which area the terminal UE is situated.With each of the networks of the list L may be associated a weightindicating an order of preference. Alternatively, the list L may containjust a single preferred network.

The list L may for example be included in a new field of the messageULA, as permitted by the Diameter protocol.

The list L can take the form of a serialized table with at least onenetwork PLMN identifier, optionally accompanied by a weightingcoefficient representing its priority relative to the other PLMNidentifiers of the list; a PLMN identifier may for example be composedof the network's MCC (Mobile Country Code) and MNC (Mobile Network Code)codes; optionally other indications may accompany each PLMN, such as thetechnologies present: 2G, 3G, 4G, 5G, WiFi, etc.

During a step E32, the mobility management entity vMME receives theacknowledgment ULA comprising the list L of preferred networks, andoptionally stores this list L if necessary so as to add it to anothermessage sent by the mobility management entity vMME.

During a step E35, the mobility management entity vMME responds to theinitial request for attachment AR of the terminal UE by a message AA towhich the list L is added. For example, the PCO (Protocol ConfigurationOption) field of the message AA can be used.

During a step E22, the base station eNB receives this response messageAA, and transmits it to the terminal UE during a step E23.

During a step E11, the terminal UE receives the message AA comprisingthe list L of preferred networks, and stores this list L. This list Lcomprises for example the identifier of a network vN-C, indicated ashaving priority over the network vN-B.

During a step E12, for example as soon as the terminal UE detects thatit is under the coverage of the network vN-C preferred to the networkvN-B by the home network hN-A, the terminal UE disconnects from thenetwork vN-B and commences a procedure for connection to the networkvN-C, by attaching itself to a base station of this network.

During an alternative step E12, the procedure for connection to thenetwork vN-C can wait for the need to appear, for example if theterminal UE has detached from the base station eNB of the network vN-Bfor any reason, and if it must reconnect, the terminal UE then commencesa procedure for connection to the visited network vN-C rather than vN-B.

FIG. 3 presents an exemplary implementation of the connection method andof the method of processing a request relating to the connection of aterminal while roaming, according to a second embodiment.

In this second embodiment, a list of preferred visited networks isprovided to the terminal by the home network during the phase ofestablishment of the IP-CAN session.

Steps E10, E20, E21 and E30 are identical to the first mode ofembodiment and are not described again.

Steps E31, E32, E40 and E41 of the first mode are replaced in thissecond mode by the steps hereinbelow.

During a step E33, once the terminal UE has been authenticated and itslocation updated, according to the earlier technique, with the homenetwork hN-A, the mobility management entity vMME sends the gateway hPGWof the home network hN-A a request CSR (Create Session Request) forIP-CAN session creation, in a known manner, for example by using theGTPv2 protocol.

This request CSR is received during a step E50 by a gateway vSWG of thevisited network vN-B, which transmits it during a step E51 to thegateway hPGW of the home network hN-A, in a known manner.

During a step E60, the gateway hPGW receives the request CSR.

During a step E61, the gateway hPGW interrogates the function hPCRF ofthe home network hN-A with a message SMR so as to ascertain thecharacteristics, also called “PCC rules”, that must be allocated to theIP-CAN session requested.

During a step E70, the function hPCRF receives the message SMR, andduring a step E71, in a novel manner, it sends the gateway hPGW amessage SMA comprising, in addition to the “PCC rules”, a list L of thenetworks that are preferred, at the time of step E71, by the networkhN-A. If it is not the function hPCRF which holds the correct list L, itobtains it for example on request from a “roaming steering” entity ofthe network hN-A.

During a step E62, the gateway hPGW receives the message SMA comprisingthe list L of preferred networks, and stores this list L.

During a step E63, the gateway hPGW responds to the initial request CSRfor IP-CAN session creation with a message CSA (Create Session Response)to which the list L is added. For example, the PCO field of the messageCSA can be used.

This response CSA is received during a step E52 by a gateway vSWG of thevisited network vN-B, which transmits it during a step E53 to themobility management entity vMME of the visited network vN-B.

During a step E34, the mobility management entity vMME receives theresponse CSA comprising the list L of preferred networks, and storesthis list L.

The following steps, E35, E22, E23, E11 and E12 are identical to thefirst embodiment and are not described again.

According to these first two embodiments, the list L is provided to theterminal UE in the context of a procedure for attachment to a basestation.

According to other embodiments, not illustrated, the list L is providedto the terminal UE in the same manner, but in the context of a TrackingArea Update, TAU, whilst the terminal UE is already attached to the basestation.

In both contexts, whether it be that of an attachment request or of aTAU request, the proposed method does indeed comprise the receipt of arequest relating to the connection of the terminal when it is beyond therange of its home network, by the mobility management entity of thevisited network (step E30) in the case of the first embodimentdescribed, or, in the case of the second mode, by the mobilitymanagement entity of the visited network (step E30) and then by the PGWgateway of the home network (step E60).

An exemplary structure of a device for connecting a terminal beyond therange of its home network (while roaming), according to one aspect ofthe invention, is now presented in conjunction with FIG. 4 .

The connection device 100 implements the connection method of a terminalwhile roaming, various embodiments of which have just been described.

Such a device 100 is implemented in a mobile terminal able to connect toa terrestrial mobile network, for example of 4G or 5G type.

For example, the device 100 comprises a processing unit 130, equippedfor example with a microprocessor μP, and driven by a computer program110, stored in a memory 120 and implementing the connection methodaccording to the invention. On initialization, the code instructions ofthe computer program 110 are for example loaded into a RAM memory,before being executed by the processor of the processing unit 130.

Such a memory 120 and such a processor of the processing unit 130 areconfigured to control:

-   a module 103 for disconnecting and reconnecting the terminal to the    priority network included in a list of at least one terrestrial    mobile network, to which the terminal must connect by priority when    it is roaming.

The device 100 also comprises:

-   a sender 101, able to send an attachment request AR, or a tracking    area update message TAUR,-   a receiver 102, able to receive an attachment response AA, or a    tracking area update acknowledgment message TAUA.

An exemplary structure of a device for processing a request relating tothe connection of a terminal beyond the range of its home network (whileroaming), according to one aspect of the invention, is now presented inconjunction with FIG. 5 .

The processing device 200 implements the method of processing a requestrelating to the connection of a terminal while roaming, variousembodiments of which have just been described.

Such a device 200 can be implemented in a mobility management entity ofa terrestrial mobile network, able to manage the location of theterminals present in its coverage, such as an MME entity, in a 4Gnetwork. The device 200 can also be implemented in a gateway forming theinterface between a terrestrial mobile network and the Internet, such asa PGW gateway, in a 4G network.

For example, the device 200 comprises a processing unit 230, equippedfor example with a microprocessor μP, and driven by a computer program210, stored in a memory 220 and implementing the processing methodaccording to the invention. On initialization, the code instructions ofthe computer program 210 are for example loaded into a RAM memory,before being executed by the processor of the processing unit 230.

Such a memory 220 and such a processor of the processing unit 230 areconfigured to control:

-   an obtaining module 202, able to obtain, on the basis of an    identifier relating to the area visited by the terminal while    roaming, a list of at least one terrestrial mobile network of the    area, to which the terminal must connect by priority.

The device 200 also comprises:

-   a receiver 201, able to receive an attachment request AR, or a    tracking area update message TAUR, or a location update response    ULA, or a session creation or modification response CSA, or a    session creation or modification request CSR (of a gateway SGW to a    PGW gateway), or a SMA message of “PCC rules” (of a PCRF function to    a PGW gateway),-   a sender 203, able to send an attachment response AA, or a tracking    area update acknowledgment message TAUA, or a location update ULR,    or a session creation or modification request CSR, or a message SMR    of request of “PCC rules” (of a PGW gateway to a PCRF function), or    a session creation or modification response CSA.

The receiver modules or sender modules described in conjunction withFIGS. 4 and 5 can be hardware modules or software modules.

FIGS. 4 and 5 illustrate only a particular way, from among severalpossible ways, of carrying out the algorithms detailed hereinabove, inconjunction with FIGS. 2 and 3 . Indeed, the proposed methods arecarried out interchangeably on a reprogrammable calculation machine (aPC computer, a DSP processor or a microcontroller) executing a programcomprising a sequence of instructions, or on a dedicated calculationmachine (for example a set of logic gates such as an FPGA or an ASIC, orany other hardware module).

In the case where the proposed methods are embedded in a reprogrammablecalculation machine, the corresponding program or programs (that is tosay the sequences of instructions) will be able to be stored inremovable storage media (such as for example a floppy disk, a CD-ROM ora DVD-ROM) or otherwise, these storage media being partially or totallyreadable by a computer or a processor.

Although the present disclosure has been described with reference to oneor more examples, workers skilled in the art will recognize that changesmay be made in form and detail without departing from the scope of thedisclosure and/or the appended claims.

What is claimed is:
 1. A connection method comprising: connecting aterminal beyond a range of the terminal's home network and in a range ofa plurality of networks in a visited area, termed visited networks, theconnecting comprising the following acts performed by the terminal:sending to a first visited network of the plurality of networks arequest to connect the terminal to the first visited network, receivingfrom the first visited network a response to the request to connect theterminal to the first visited network, the response comprising a list ofat least one network of the plurality of networks, to which the terminalmust connect by priority, without sending a request for the list,storing the list in a computer-readable memory, and disconnecting theterminal from the first visited network and connecting the terminal to asecond visited network of the stored list.
 2. The connection method asclaimed in claim 1, comprising, after storing the list, detecting by theterminal that the terminal is in the range of the second visited networkof the stored list, and then performing the act of connecting to thesecond visited network of the stored list in whose range the terminalhas detected to be.
 3. The connection method as claimed in claim 1,wherein, after storing the list, performing the acts of disconnectingthe terminal from the first visited network and connecting the terminalto the second visited network of the stored list, which comprises:detaching the terminal from the first visited network followed byconnecting the terminal to the second visited network.
 4. The connectionmethod as claimed in claim 1, where the request to connect is a requestfor attachment of the terminal to a base station of the visited network.5. The connection method as claimed in claim 1, where the list isencrypted with a key previously shared between the terminal and the homenetwork, the key allowing a verification of integrity of the list.
 6. Adevice comprising: a sender configured to send a request to connect aterminal beyond a range of the terminal's home network and in a range ofa plurality of networks in a visited area, to a network of the pluralityof networks, termed first visited network, a receiver configured toreceive from the first visited network a response to the request toconnect the terminal to the first visited network, the responsecomprising a list of at least one priority network of the plurality ofnetworks, to which the terminal must connect by priority, withoutsending a request for the list, and a processor configured to store thelist in a computer-readable memory and to disconnect the terminal fromthe first visited network and connect the terminal to a second networkof the stored list.
 7. The device as claimed in claim 6, where theprocessor is further configured to, after storing the list, detect thatthe terminal is in the range of the second visited network of the storedlist, and to connect the terminal to the second visited network of thestored list which is the network in whose range the terminal hasdetected to be.
 8. The device as claimed in claim 6, where the processoris further configured to, after memorizing the list, detach the terminalfrom the first visited network before connecting the terminal to thesecond visited network of the stored list.
 9. The device as claimed inclaim 6, where the request to connect is a request for attachment of theterminal to a base station of the first visited network.
 10. The deviceas claimed in claim 6, where the list is encrypted with a key previouslyshared between the terminal and the home network, the key allowing averification of integrity of the list.
 11. A non-transitorycomputer-readable medium comprising a computer program stored thereon,comprising instructions for implementing a method of connecting aterminal beyond a range of the terminal's home network and in a range ofa plurality of networks in a visited area, termed visited networks, whenthis program is executed by a processor of the terminal, wherein theinstructions configure the terminal to perform acts comprising: sendingto a first visited network of the plurality of networks a request toconnect the terminal to the first visited network, receiving from thefirst visited network a response to the request to connect the terminalto the first visited network, the response comprising a list of at leastone network of the plurality of networks to which the terminal mustconnect by priority, without sending a request for the list, storing thelist in a computer-readable medium, and disconnecting the terminal fromthe first visited network and connecting the terminal to a secondvisited network of the stored list.
 12. The non-transitorycomputer-readable medium as claimed in claim 11, wherein theinstructions further configure the terminal to, after storing the list,detect that the terminal is in the range of the second visited networkof the stored list, and then perform the act of connecting to the secondvisited network of the stored list in whose range the terminal hasdetected to be.
 13. The non-transitory computer-readable medium asclaimed in claim 11, wherein the instructions configure the terminal to,after storing the list, perform the acts of disconnecting the terminalfrom the first visited network and connecting the terminal to the secondvisited network of the stored list, which comprises: detaching theterminal from the first visited network followed by connecting theterminal to the second visited network.
 14. The non-transitorycomputer-readable medium as claimed in claim 11, where the request toconnect is a request for attachment of the terminal to a base station ofthe visited network.
 15. The non-transitory computer-readable medium asclaimed in claim 11, where the list is encrypted with a key previouslyshared between the terminal and the home network, the key allowing averification of integrity of the list.